Migration imaging method involving solvent wash-away of unmigrated particles

ABSTRACT

A migration imaging system wherein an imaging member typically comprising a softenable layer, migration marking material, and a supporting substrate, is provided, an electrical latent image is formed thereon, and the latently imaged member is softened whereby the marking material migrates in depth in the softenable layer in imagewise configuration toward the substrate. This member is then more fully developed by substantially uniformly recharging in the presence of activating electromagnetic radiation and by removing the background and residual materials.

United States Patent Gundlach 1 51March 13, 1973 I 1 MIGRATION IMAGING METHOD 3,457,070 7/1969 Watanabe etal ..96/l.4

INVOLVING SOLVENT WASH-AWAY 3,520,68l 7 1970 Goffe 0 UNMIGRATED PARTICLES 3,525,612 8/1970 11015161111 ..96/l

3,556,783 1 1971 Kyriakakis ..96/l.2

Continuation-in-part of Ser. No. 851,872, Aug. 21, 1969, Pat. No. 3,648,607.

us. c1 ..96/l R, 96/13, 96/l.4,

117/1.7,117/17.5 LE, 117/218 1111.01. ..G03g 5/00, 003,; 13/20, 003 13/22 Field of Search ..96/l, 1.2, 1.8, 1.4

References Cited UNITED STATES PATENTS 4/1969 Tanaka et al ..355/ll Primary Examiner-George F. Lesmes Assistant Examiner-M. B. Wittenberg Attorney-James J. Ralabate, David C. Petre and Roger W. Parkhurst A migration imaging system wherein an imaging member typically comprising a softenable layer, migration marking material, and a supporting substrate, is provided, an electrical latent image is formed thereon, and the latently imaged member is softened whereby the marking material migrates in depth in the softenable layer in imagewise configuration toward the substrate. This member is then more fully developed by substantially uniformly recharging in the presence of activating electromagnetic radiation and by removing the background and residual materials.

ABSTRACT 26 Claims, 7 Drawing Figures PATENTEDHAR] 31973 3720513 WWW-4 2 F/azb INVENTOR. ROBERT W. GUNDLACH ATTORNEY MIGRATION IMAGING METHOD INVOLVING SOLVENT WASH-AWAY OF UNMIGRATED PARTICLES CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of my copending application Ser. No. 851,872, filed Aug. 21, 1969, now U.S. Pat. No. 3,648,607.

BACKGROUND OF THE INVENTION This invention relates in general to imaging, and more specifically to migration imaging wherein a migration marking material is selectively moved through a softenable medium.

Recently, a migration imaging system capable of producing high quality images of high density, continuous tone, and high resolution has been developed. Such migration imaging systems are disclosed in copending applications Ser. No. 837,780, filed June 30, 1969, and Ser. No. 837,591, filed June 30, 1969. In a typical embodiment of the new migration imaging system an imaging member comprising a substrate, a layer of softenable material and electrically photosensitive marking material is latently imaged by electrically charging the member and exposing the charged member to a pattern of activating electromagnetic radiation such as light. Where the photosensitive migration marking material was originally in the form of a fracturable layer at the upper surface of the softenable layer, the marking particles in the exposed areas of the member migrate toward the substrate when the member is developed by softening the softenable layer.

softenable as used herein is intended to mean any material which can be rendered more permeable thereby enabling particles to migrate through its bulk. Conventionally, changing permeability is accomplished by dissolving, melting, and softening as by contacting with heat, vapors, partial solvents, solvent vapors, solvents and combinations thereof, or by otherwise reducing the viscosity of the material.

Fracturable" layer or material as used herein, means any layer or material which is capable of breaking up during development, thereby permitting portions of said layer to migrate toward the substrate or to be otherwise removed. The fracturable layer may be particulate, semi-continuous, or continuous in various embodiments of the migration imaging members. Such fracturable layers of marking material are typically contiguous the surface of the softenable layer spaced apart from the substrate, and such contiguous layers may be near, at, coated onto, or slightly, partially or substantially embedded in the softenable layer in various embodiments of the imaging members of the inventive system. Contiguous," for the purpose of this invention is defined as in Websters New Collegiate Dictionary, Second Edition, 1960: In actual contact; touching; also, near, though not in contact; adjoining.

There are various other systems for forming such images, wherein non-photosensitive or inert, marking materials are arranged in the aforementioned fracturable layers, or dispersed throughout the softenable layer in a binder configuration, as described in the aforementioned copending applications which also disclose a variety of methods which may be used to form latent images upon such migration imaging members.

Likewise, various means for developing latent images in the novel migration imaging system are known. Typical development methods include solvent wash-away; solvent vapor softening, heat softening and combinations of these methods. In the solvent washaway method, the migration marking material migrates in imagewise configuration toward the substrate through the softenable layer as it is softened and dissolved, leaving an image of migrated particles corresponding to the desired image pattern on the substrate with the material of the softenable layer substantially completely washed away. In the heat or vapor softening modes, the softenable layer is softened to allow imagewise migration of marking material toward the substrate and the developed imaged member generally comprises the substrate having migrated marking particles near the softenable layer-substrate interface, with the softenable layer and unmigrated marking materials intact on the substrate in substantially their original condition.

Various methods and materials and combinations thereof have previously been used to fix unfixed migration images. For example, fixing methods and materials previously used are disclosed in copending applications Ser. No. 590,959, filed Oct. 31, 1966 now abandoned, and Ser. No. 695,214, filed Jan. 2, 1968 now abandoned.

In new and growing areas of technology such as the migration imaging systems of the present invention, new methods, apparatus, compositions of matter, and articles of manufacture continue to be discovered for the application of the new technology in new modes. The present invention relates to a new and advantageous system for the development of latent images in such migration imaging systems.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide novel migration imaging system.

It is another object of this invention to provide a novel imaging system wherein an electrically photosensitive marking material is selectively displaced in image configuration.

It is another object of this invention to provide a system for the development of latent images in migration imaging members.

It is a further object of this invention to provide a system for increasing the bonding forces attracting the migration imaging material to the substrate in imaged migration imaging members.

It is a further object of this invention to provide a system for increasing the latitude of development conditions in the development of migration imaging members.

It is yet another object of this invention to increase the edge sharpness between imaged and non-imaged areas in a migration imaging member.

It is yet another object of this invention to provide a system for improving the resolution of migration images. i

It is still another object of this invention to provide a migration imaging system more suitable for use in a system wherein the electrical latent image, from which the visible migration image is formed, may be produced in a more practical device such as a portable camera.

The foregoing objects and others are accomplished in accordance with this invention by a migration imaging system wherein a migration imaging member comprising a softenable layer and migration marking material is provided, having an electrical latent image thereon, and said latently imaged member is partially developed by softening the softenable layer. When it is desired to fully develop the imaged member, said member is then typically uniformly recharged in the presence of ambient light, and is fully developed by removing the background and residual materials.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed disclosure of the preferred embodiments of the invention taken in conjunction with the accompanying drawings thereof, wherein:

FIG. 1 is a partially schematic, cross-sectional view ofa migration imaging member preferred for use in the inventive system.

FIG. 2 illustrates in partially schematic, cross-sectional views a preferred embodiment of the advantageous migration imaging process of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 a migration imaging member preferred for use in the advantageous system of the present invention is illustrated, wherein imaging member comprises a softenable layer 11 having electrically photosensitive particles 12 dispersed throughout the softenable layer in a binder layer configuration. In the embodiment illustrated in FIG. 1, the migration imaging member is shown upon substrate 13. It is noted that although the composite imaging member 10 illustrated in FIG. 1 shows a softenable layer 11 already in contact with conductive substrate 13, the migration imaging member comprising the softenable layer having electrically photosensitive particles dispersed therein may, alternatively, be self-supporting and brought into contact with any substrate which is suitable for use in the inventive system.

Referring now more specifically to the individual elements illustrated in FIG. 1, the substrate 13 generally facilitates the charging or sensitization of the member according to the optimum electrical-optical mode of the invention when the substrate is electrically conductive. Typically this substrate may be of copper, brass, nickel, zinc, chromium, stainless steel, conductive plastics and rubbers, aluminum, steel, cadmium, silver, gold or paper rendered conductive by the inclusion of a suitable chemical therein or through conditioning in a humid atmosphere to insure the presence therein of sufficient water content to render the material conductive.

In various other embodiments, the substrate 13 may be less electrically conductive, or substantially electrically insulating. A number of substrates suitable for use in the imaging members of the present invention are disclosed in copending applications, Ser. No. 837,780 and Ser. No. 837,591, both filed June 30,1969, and the disclosures of both applications are hereby expressly incorporated by reference in the present specification.

The substrate 13 may be in any suitable form such as a metallic strip, sheet, plate, coil, cylinder, drum, endless belt, moebius strip, circular disc, or the like. If desired, the conductive substrate may be coated on an insulator such as paper, glass, or plastic. Examples of this type of substrate are a substantially transparent tin oxide coated glass available under the trademark NESA" from the Pittsburgh Glass Company, aluminized polyester film, available under the trademark "Mylar" film DuPont, or Mylar coated with copper iodide.

Softenable layer 11, which may comprise one or more layers of softenable materials, may be any suitable material, typically a plastic or thermoplastic material, which is softenable for example, in a solvent liquid, solvent vapor, heat or combinations thereof. In addition, for the optimum electrical-optical mode of the advantageous system of the present invention, the softenable layer 11 is typically substantially electrically insulating during the migration force applying and softening steps at least until the migration has been initiated. Where the softenable layer is to be dissolved either during or after imaging, it should be soluble in a solvent which does not also attack the migration marking particles 12.

Typical softenable materials include Staybelite Ester 10, a partially hydrogenated rosin ester, Foral Ester, a hydrogenated rosin triester, and Neolyne 23, an alkyd resin, all from Hercules Powder Co.; SR type silicone resins available from General Electric Corporation; Sucrose Benzoate, Eastman Chemical; Velsicol X-37, a polystyrene-olefin copolymer from Velsicol Chemical Corp.; Hydrogenated Piccopale 100, Piccopale H-2, highly brached polyolefins, Piccotex 100, a styrenevinyl toluene copolymer, Piccolastic A-75, A-50, E-50, and all polystyrenes, Piccodiene 2215, a polystyrene-olefin copolymer, all from Pennsylvania Industrial Chemical Corp.; Nirez 1085, a polyterpene resin from Tenneco Chem., Inc.; Araldite 6060 and 6071, epoxy resins from Ciba; R5061A, a phenylmethyl silicone resin, from Dow Corning; Epon 1001 a bisphenol A-ephichlorohydrin epoxy resin, from Shell Chemical Corp.; and PS-2, PS-3, both polystyrenes, and ET-693, a phenol-formaldehyde resin, from Dow Chemical; custom synthesized copolymers of styrene and hexylmethacrylate, a custom synthesized polydiphenylsiloxane; a custom synthesized polyadipate; acrylic resins available under the trademark Acryloid from Rohm & Haas Co., and available under the trademark Lucite from the E. I. DuPont de Nemours & Co.; thermoplastic resins available under the trademark Pliolite from the Goodyear Tire & Rubber Co.; a chlorinated hydrocarbon available under the trademark Aroclor from Monsanto Chemical Co.; thermoplastic polyvinyl resins available under the trademark Vinylite from Union Carbide Co.; other thermoplastics disclosed in Gunther et al. US. Pat. No. 3,l96,0l l; waxes and blends, mixtures and copolymers thereof.

The above group of materials is not intended to be limiting, but illustrative of materials suitable for softenable layer 11 more of which may be disclosed in the incorporated disclosures. The softenable layer may be of any suitable thickness, with the thicker layers generally requiring greater electrical potentials in the optimum and preferred modes of this invention. The

softenable layer is preferably of a thickness in the range between about 1% micron and about 16 microns. Softenable layer 12 may be formed by any suitable method including dip coating, roll coating, gravure coating, vacuum evaporation, and other techniques.

Although the softenable layer 13 is typically formed on a suitable substrate, in some embodiments, the softenable layer may itself possess sufficient integrity to be self-supporting. Such self-supporting imaging members may themselves be imaged. However, typically the selfsupporting softenable layered imaging member is brought into contact with a suitable substrate before or during the imaging process.

The electrically photosensitive particles 12, portions of which migrate during image formation, may comprise any suitable electrically photosensitive particles which are not substantially degraded by the softening medium used to soften binder layer 11 in the development process. Electrically photosensitive particles as used herein refers to any particles which when dispersed in a soluble, electrically insulating binder layer as described herein, in response to electrical charging, imagewise exposure to activating radiation and softening of said binder layer, are caused to selectively deposit in image configuration on a substrate.

While photoconductive particles, (and photoconductive is used in its broadest sense to mean particles which show increased electrical conductivity when illuminated with electromagnetic radiation and not necessarily those which have been found to be useful in xerography in xerographic pigment-binder plate configurations) have been found to be class of particles useful as electrically photosensitive particles in this invention, and while the photoconductive effect is often sufficient in the present invention to provide an electrically photosensitive particle, it does not appear to be a necessary effect. Apparently the necessary effect according to the invention is the selective relocation of charge into, within or out of the particles, said relocation being effected by light action on the bulk or the surface of the electrically photosensitive particle, by exposing said particle to activating radiation, which may specifically include photoconductive effects, photoinjection, photoemission, photochemical effects and others which cause selective relocation of charge.

Electrically photosensitive particles 12 may comprise any suitable inorganic or organic material. Typical inorganic materials are vitreous selenium, vitreous selenium alloyed with arsenic, tellurium, antimony, or bismuth, etc.; cadmium sulfide, zinc oxide, cadmium sulfoselenide, and many others. U.S. Pat. No. 3,121,006 to Middleton et al. admirably sets forth a whole host of typical inorganic photosensitive pigments. Typical organic materials are: Watchung Red B, a barium salt of l-(4-methyl-5'-chloro-azobenzene-2'- sulfonic acid)-2 hydrohydroxy-3-naphthoic acid, C. I. No. 15865, available from DuPont; lndofast double scarlet toner, a Pyranthrone-type pigment available from Harmon Colors; quindo magenta RV-6803; a quinacridone-type pigment available from Harmon Colors; Cyan Blue, GTNF the beta form of copper phthalocyanine, C. I. No. 74160, available from Collway Colors; Monolite Fast Blue GS, the alpha form of metal-free phthalocyanine, C. I. No. 74100, available from Arnold Hoffman Co.; Diane Blue, 3,3 '-methoxy- 4,4'-diphenyl-bis(1"azo-2 "-hydroxy-3 '-naphthanilide), C. I. No. 21180, available from Harmon Colors; and Algol G.C., 1,2,5,6-di (D,D'-diphenyl)-thiazoleanthraquinone, C. I. No. 67300, available from General Dyestuffs; Naphthol Red B, 1-(2-methoxy-5'- nitrophenylazo)-2-hydroxy-3 '-nitro-3-naphthonilide, available from Collway Colors; and lndofast Yellow Toner, a flavanthrone, available from Harmon Colors. A particularly preferred photosensitive pigment which gives outstanding results is the x form of metal-free phthalocyanine produced by the method set forth in copending application Ser. No. 505,723, filed Oct. 29, 1965, now U.S. Pat. No. 3,357,989. The above list of organic and inorganic materials is illustrative of some of the typical materials, and should not be taken as a complete listing of photosensitive materials suitable for use in the present invention.

The particle size for the migration marking particles dispersed in the binder structure migration imaging member is typically not greater than about 2 microns. Submicron particles give even more preferred results. Practically, it may be difficult to produce or measure particles of a size less than about 0.02 microns. An optimum range of particle sizes is the range between about 0.02 microns and about 0.5 microns. The small particles give migration images which have better resolution and image densities than larger particles, although larger particles, even those greater in size than 2 microns may produce satisfactory images in the inventive system.

In FIG. 2 the various process steps of a preferred embodiment of the advantageous system of the present invention are illustrated on cross-sectional views of the preferred imaging member of FIG. 1. In FIG. 2 (a) the imaging member is shown being electrically charged by the preferred means of electrostatically charging by corona charging device 14 which electrically conductive substrate 13 is grounded 15. This charging step typically substantially uniformly charges the imaging member at the surface of binder layer 11, and typically induces corresponding opposite charge at the interface between substrate 13 and binder layer 11. Where the imaging member includes electrically photosensitive materials, this charging step is typically carried out in the absence of extraneous activating electromagnetic radiation, i.e. under darkroom conditions. Although positive charges are illustrated in FIG. 2(a), charge of either polarity, as desired, may be used in various embodiments of the inventive system. In FIG. 2(b) the uniformly charged imaging member is shown being exposed to an image pattern of activating electromagnetic radiation here for example light illustrated as emanating from source 16 which produces a light-andshadow image pattern on the uniformly charged surface of the imaging member because said member is illuminated only in those areas where optical mask 17 allows the activating radiation to pass through it. In the light struck areas 18 the electrically photosensitive particles 12 within the binder layer I] allow the electrostatic charge formerly on the surface of the imaging member to dissipate, while the electrostatic charge in unexposed areas 19 remains on the surface of said member. In this way an electrical latent image is provided on the imaging member.

The term electrical latent image and of several variant forms thereof used herein includes the images formed by the charge-expose mode hereof which cannot readily be detected by standard electromagnetic techniques as an electrostatic image, for example, of the type found in xerography, so that no readily detectable or at best a very small exchange in the electrostatic or coulombic force is found after exposure (when using preferred exposure levels); an electrostatic latent image of a type similar to those found in xerography which are typically readily measurable by standard electrometers, that is the electrostatic latent images show a surface potential typically reading of at least about to 10 volts.

It will be appreciated that in addition to the optimum electrical-optical mode, electrical latent images may be formed on the imaging member illustrated in FIG. 1, and preferred for use in the advantageous system of the present invention, by any means suitable for producing an electrical latent image on such a member. Other modes include charging or sensitizing an image configuration through the use of a mask or stencil, or by first forming such a charge pattern on a separate photoconductive insulating layer according to conventional xerographic production techniques and then transferring this charge pattern to the surface of the migration imaging member by bringing the two into very close proximity and utilizing breakdown techniques as described, for example, in Carlson U.S. Pat. No. 2,982,647 and Walkup U.S. Pat. No. 2,825,814 and No. 2,937,943. In addition, charge patterns conforming to selected shaped electrodes or combinations of electrodes may be formed on the migration imaging member by the TESI" discharge technique, as more fully described in Schwartz U.S. Pat. No. 3,023,731 and 2,919,967 or by techniques described in Walkup U.S. Pat. No. 3,001,848 and No. 3,001,849, as well as by electron beam recording techniques, as described in Glenn U.S. Pat. No. 3,113,179. Various other modes of creating electrical latent images are described in the incorporated disclosures and in copending application Ser. No. 327, filed Jan. 2, 1970, now abandoned which is also hereby expressly incorporated by reference.

In FIG. 2(a) the imaging member having the electrostatic latent image thereon is softened by the application of a suitable softening medium such as solvent vapors or heat or combinations thereof, and as softenable layer 12 becomes permeable to the electrically photosensitive marking material particles 12, the electrically photosensitive marking particles in the charged areas 19 of the electrostatic latent image migrate in imagewise configuration toward the interface between substrate 13 and binder layer 11. In the exposed areas 18 the electrically photosensitive particles remain dispersed throughout binder layer 11 in substantially the same fashion in which they were oriented in the original migration imaging member.

In the disclosures already incorporated by reference herein, a host of softening medias and methods is disclosed for use in the inventive system.

With the imaged migration imaging member in the configuration illustrated in FIG. 2(c), it has been found that the imaging member may be handled and exposed to ambient light without detrimental effects to the image. This is especially so where the softenable material has been hardened to its normal viscosity after the initial softening step. The imaged member in this condition may be stored indefinitely, and later may be fully developed by the methods described in conjunction with FIGS. 2(d) and 2(e).

In FIG. 2(d), the imaged migration imaging member described in FIG. 2(c) is shown being electrostatically charged with corona charging device 14, here a substantially uniform recharging step substantially identical to the step shown in FIG. 2(a). However, this electrostatic charging step illustrated in FIG. 2(d) is performed in the presence of substantially uniform activating illumination. While charging in room light, it has been found that the electrostatic charge appears uniformly across the surface of areas 19 where the electrically photosensitive marking particles 12 have previously migrated to the interface between substrate 13 and binder layer 11. However in areas 18, where the electrically photosensitive particles are still dispersed throughout binder layer 11, the activating illumination produces sufficient electrical conductivity among the electrically photosensitive particles 12 within exposed areas 18, to prevent a buildup of electrostatic charge on the surface of the imaged migration imaging member. Therefore, the substantially uniform deposition of electrostatic charge created by corona charging device 14 is effective to substantially charge the surface of the imaged migration imaging member only in the unexposed image areas 19.

In FIG. 2(e) the imaged migration imaging member recharged as illustrated in FIG. 2(d), is shown being rinsed, or wash-away developed, in a bath of solvent 20, suitable for dissolving softenable layer 11 but incapable of substantially degrading the migration marking material 12. The wash-away development step is carried out in a bath 20 in any suitable container 21, and the dissolving softenable layer and unmigrated migration marking material 12 are shown dissolving away from the imaging member at 22. In unexposed image areas 19 where the recharging step of FIG. 2(d) was effective to create an electrical field across the migrated image portion of the imaged migration imaging member, the electrically photosensitive marking particles which migrated in image configuration 23 adhere to substrate 13 in the same imagewise configuration.

Surprisingly, it has been found that the steps of electrically recharging the imaged migration imaging member, as illustrated in FIG. 2(d) and thereafter wash-away developing as illustrated in FIG. 2(e) apparently enhance the combination of surface attractive forces and electrical attractive forces between the electrically photosensitive marking particles 12 which migrated in unexposed image areas 19 and the substrate itself. At the same time, however, the recharging step in ambient illumination does not affect the background areas of the desired image because the recharging step is performed in the presence of ambient illumination whereby no significant electrical field is created across the exposed portions of the imaged member. Because the attractive forces between migrated marking particles and the substrate are apparently enhanced, the imaging system produces images having low background and sharper resolution.

In addition, the latitude of development conditions particularly in the wash-away development mode, is expanded.

In FIG. 2(f), the fully, wash-away developed migration imaging member produced by the advantageous system of the present invention is illustrated comprising the electrically photosensitive marking material 12 in imagewise configuration 23 on the surface of conductive substrate 13. This fully developed, migration imaging member is then suitable for use in any process whereby the image is fixed to the substrate, where such fixing is desirable. For example, methods of fixing migration images to substrates are disclosed in copending applications Ser. No. 590,959, filed Oct. 31, 1966, now abandoned and Ser. No. 695,214, filed Jan. 2, 1968, now abandoned.

The following examples further specifically define the present invention with respect to the development of migration imaging members. The parts and percentages are by weight unless otherwise indicated. The examples below are intended to illustrate various preferred embodiments of the novel migration image development system.

EXAMPLE I A migration imaging member is prepared by placing a mixture of about 5 percent by weight x-form metalfree phthalocyanine with about 95 percent Nirez 1085, a polyterpene resin available from Tenneco Chemical, Inc., and by diluting this mixture with about an equal amount of Sohio 3454 Odorless Solvent, available from Standard Oil Co. of Ohio. This mixture is then ball milled for about an hour to disperse the phthalocyanine throughout the diluted resin. This mixture is then coated over a thin aluminum metal substrate and the solvent is allowed to evaporate leaving an about 6 micron thick binder layer of phthalocyanine dispersed in the polyterpene resin softenable layer.

This imaging member is then substantially uniformly positively electrostatically charged in a Model D Processor, available from Xerox Corporation, Rochester, N.Y., and the charged member is then exposed to a light-and-shadow image pattern at an exposure level of about 1/30 f.c.s. The charged and exposed member is then developed by immersing the member in a bath of liquid trichloroethylene and the member is gently agitated to facilitate removal of the excess imaging materials. The trichloroethylene liquid softens the polyterpene softenable layer and the phthalocyanine migration marking particles in the unexposed areas migrate to the substrate in imagewise configuration, and the trichloroethylene solvent then removes substantially all of the remaining softenable layer and migration marking particles. It is found that the above described wash-away development produces high background images when there is too little agitation, and that too violent agitation removes desirable portions of the image. The images produced by this method are dense and of good quality but resolution is somewhat limited by a fringe deposit of migration marking particles near larger dense image areas on the substrate.

EXAMPLE n An imaging member is provided as described in Example I and is charged and exposed as in Example I. The charged and exposed imaging member is then exposed to trichloroethylene vapors for about I to 2 seconds. The trichloroethylene vapors soften the softenable polyterpene resin layer and the phthalocyanine migration marking particles in the unexposed image areas migrate in depth in the softenable layer toward the substrate in imagewise configuration. After the exposure to the trichloroethylene vapors, the member is removed from the solvent vapors and the softenable layer regains its harder, more viscous condition. This vapor developed imaging member is then charged a second time as described in Example I, and is, either simultaneously with the charging or after the charging, substantially uniformly exposed to room light. This recharged and exposed imaging member is then washaway developed as described in Example I. The resultant image exhibits lower background and better resolution than the image produced by Example I. It is also found that development time and the character of the agitation used in the wash-away development mode are much less critical than in the system described in Example I.

EXAMPLE III An imaging member is prepared in Example I except that the ratio of x-form metal-free phthalocyanine to Nirez polyterpene resin is increased to about 15:85. This member is imaged as described in Example II except that vapor development time is increased to about 20 seconds. The resultant image is like that described in Example II.

EXAMPLE IV An imaging member is prepared as in Example I, except that in about 5 micron thick layer of Nirez polyterpene resin is coated directly onto the aluminum substrate, and an about 3 micron layer of the phthalocyanine-Nirez binder mixture is coated over the Nirez softenable layer. This member is imaged as described in Example III and produces a resultant image like that described in Example II.

EXAMPLE V A binder structured imaging member according to the present invention is prepared by mixing the coating comprising about I00 parts by weight Nirez 1085, a polyterpene resin from Tenneco Chemicals, Inc.; about 15 parts x-form metal-free phthalocyanine; about parts Sohio 3454, a refined kerosene from the Standard Oil Company of Ohio; about 20 parts Kynar, vinylidene fluoride available from the Pensal Chemical Corp., and about 4 parts 2,6-di-tert-butyl-p-cresol, an anti-oxidant which reduces aging, available from the Eastman Kodak Co., Rochester, N.Y. The coating mix is blended for about 2 hours and 20 minutes in a ball mill Red Devil paint shaker having about it; inch steel milling balls. The prepared coating is roll coated onto a conductive substrate of about 5 mil aluminum foil available from American Lamotite Corp., using a No. 3 wire wound Meier rod. The freshly coated substrate is then oven dried for about 1 hour at about 50C. This imaging member is then suitable for imaging in the charge-expose mode of the present invention as described in Example VII and this system produces lithographic printing masters.

EXAMPLE VI A binder structure imaging member suitable for use in the present invention is produced by preparing a coating comprising about 100 parts Nirez, about 15 parts x-form metal-free phthalocyanine, about 100 parts Sohio 3440 solvent, and about 25 parts polystyrene resin of molecular weight of about 30,000 and blending the coating mixture for about 2 9i hours in a ball mill. The blending reduces the polystyrene particle size to about 1 or 2 microns. The prepared coating is then roll coated onto a substrate comprising an AB. Dick aluminum offset plate of thickness of about 0.0035 inch available from A. B. Dick Duplicating Products, Chicago, Ill., the roll coating being accomplished with a No. 6 wire wound Meier rod. The coated member is then oven dried for about 45 minutes at about 65C.

The imaging member produced in this way includes inert fusable particles which are substantially transparent and which thereby allow light impinging upon the imaging member during the charge-expose mode of imaging, to be transmitted through said inert particles which may be located between the source of radiation and the photosensitive particles in the imaging member. This member is suitable for imaging for use as a lithographic printing master.

EXAMPLE VII Using the structure of Example II, with the substrate of the member electrically grounded, the member is corona charged under darkroom conditions to a positive potential of about 200 volts. After or during charging an image pattern of activating electromagnetic radiation, here visible light, is projected onto the surface of the member, thereby selectively discharging the member in the exposed areas. The member is then exposed to an atmosphere of air saturated with trichloroethylene vapors, which exposure is performed for about seconds while the member is still under darkroom conditions. The member is then removed from trichloroethylene atmosphere and allowed to dry in ambient room light for at least about 5 seconds, and the member is then again corona charged in ambient room light with a charging current equal to the initial sensitizing charge. The recharged member is then immersed in a gently agitated bath of trichloroethylene for about 10 seconds, during which time the Nirez is substantially dissolved and rinsed away and carries with it the unmigrated particles of phthalocyanine and polystyrene from the areas illuminated during the image exposure step, while the migration particles in the unexposed areas adhere to the substrate. The member is removed from the rinse developing bath and heated to about 200C for about 10 seconds. This heating step softens the polystyrene particles which fuse together thereby forming a binder structure throughout the image areas. The member is cooled to room temperature and then comprises a tough, visible, positive-to-positive reproduction of the original image in raised image configuration on the substrate. This member is suitable for use as an offset lithographic printing master.

What is claimed is: 1. An imaging method comprising: providing a partially imaged migration imaging member comprising a softenable layer having unmigrated electrically photosensitive marking material dispersed throughout portions of said softenable layer wherein the marking material is unmigrated, and having such electrically photosensi tive marking material migrated at least in depth away from one surface of said softenable layer in the migrated portions of said softenable layer,

electrically charging the surface of the imaging member while said member is substantially uniformly exposed to activating electromagnetic radiation,

placing the opposite surface of said softenable layer in contact with a substrate, and contacting said imaging member with a liquid solvent for said softenable material whereby the migrated marking material completes its migration to the substrate in image configuration, and the softenable material and the unmigrated portions of the migration marking material are removed from said imaging member. 2. An imaging method according to claim 1 comprising:

providing a partially imaged migration imaging member comprising a softenable layer on a substrate, said softenable layer having unmigrated electrically photosensitive marking material dispersed throughout unmigrated portions of said softenable layer, and having such electrically photosensitive marking material migrated at least in depth away from the surface of said softenable layer spaced apart from said substrate in the migrated portions of said softenable layer,

electrically charging the surface of the imaging member while said member is substantially uniformly exposed to activating electromagnetic radiation, and

contacting said imaging member with a liquid solvent for said softenable material whereby the softenable layer and the unmigrated portions of the migration marking material are removed from said imaging member.

3. The method of claim 1 wherein the electrical charging step comprises electrostatically charging said member.

4. The method of claim 1 wherein said substrate is an electrically conductive substrate.

5. The method of claim 1 wherein said substrate is substantially electrically insulating.

6. The method of claim 1 wherein said softenable layer is of thickness in the range between about /5 micron and about 16 microns.

7. The method of claim 1 wherein said photosensitive marking material comprises particles of a size not greater than about 2 microns.

8. The method of claim 7 wherein said photosensitive marking particles are of a size in the range between about 0.02 microns and about 0.5 microns.

9. The method of claim 1 wherein said photosensitive marking material comprises x-form metal-free phthalocyanine.

10. The method of claim 1 wherein said migration imaging member additionally comprises a second layer comprising softenable material, said second layer disposed between the substrate and the softenable layer having the marking particles dispersed therein.

ill. An imaging method comprising: providing a migration imaging member comprising a softenable layer having electrically photosensitive marking material dispersed throughout said softenable layer, providing an electrical latent image upon said imaging member, softening the softenable layer whereby migration marking material migrates in depth in imagewise configuration in said softenable layer away from one surface of said softenable layer, then electrically charging said surface of the imaging member while said member is substantially uniformly exposed to activating ,electromagnet radiation, placing the opposite surface of the softenable layer in contact with a substrate, and contacting said imaging member with a liquid solvent for said softenable material whereby the migrated marking material completes its migration to the substrate in image configuration, and the softenable layer and the unmigrated portions of the migration marking material are removed from said imag ing member. 12. An imaging method according to claim 11 comprising:

providing a migration imaging member comprising a softenable layer having electrically photosensitive marking material dispersed throughout said softenable layer and said softenable layer in contact with a substrate, providing an electrical latent image upon said imaging member, softening the softenable layer whereby migration marking material migrates in depth in said softenable layer toward said substrate in imagewise configuration, electrically charging the surface of the imaging member while said member is substantially uniformly exposed to activating electromagnetic radiation, and contacting said imaging member with a liquid solvent for said softenable material whereby the softenable layer and the unmigrated portions of the migration marking material are removed from said imaging member.

13. The method of claim 11 wherein said electrical latent image is an electrostatic latent image.

14. The method of claim 11 wherein the electrical recharging step comprises electrostatically charging said member.

15. The method of claim 11 wherein said softenable layer is softened by exposing the imaging member to solvent vapors capable of softening said softenable layer.

16. The method of claim 11 wherein said softenable layer is softened by the application of heat sufficient to soften said softenable layer.

17. The method of claim 11 wherein after said softenable layer is softened, said softenable layer is substantially returned to its initial viscosity.

18. The method of claim 11 wherein said substrate is an electrically conductive substrate.

19. The method of claim 11 wherein said substrate 18 substantially electrically insulating.

20. The method of claim 11 wherein said softenable layer is of thickness in the range between about 7% micron and about 16 microns.

21. The method of claim 11 wherein said photosensitive marking material comprises particles of a size not greater than about 2 microns.

22. The method of claim 1 1 wherein said photosensitive marking particles are of a size in the range between about 0.02 microns and about 0.5 microns.

23. The method of claim 11 wherein said photosensitive marking material comprises x-form metal-free phthalocyanine.

24. The method of claim 11 wherein said imagin member additionally comprises a second layer comprising softenable material, said second layer disposed between the substrate and the softenable layer having the marking particles dispersed therein.

25. The imaging method of claim 1 wherein the softenable layer is substantially electrically insulating.

26. The imaging method of claim 1 1 wherein the softenable layer is substantially electrically insulating. 

1. An imaging method comprising: providing a partially imaged migration imaging member comprising a softenable layer having unmigrated electrically photosensitive marking material dispersed throughout portions of said softenable layer wherein the marking material is unmigrated, and having such electrically photosensitive marking material migrated at least in depth away from one surface of said softenable layer in the migrated portions of said softenable layer, electrically charging the surface of the imaging member while said member is substantially uniformly exposed to activating electromagnetic radiation, placing the opposite surface of said softenable layer in contact with a substrate, and contacting said imaging member with a liquid solvent for said softenable material whereby the migrated marking material completes its migration to the substrate in image configuration, and the softenable material and the unmigrated portions of the migration marking material are removed from said imaging member.
 2. An imaging method according to claim 1 comprising: providing a partially imaged migration imaging member comprising a softenable layer on a substrate, said softenable layer having unmigrated electrically photosensitive marking material dispersed throughout unmigrated portions of said softenable layer, and having such electrically photosensitive marking material migrated at least in depth away from the surface of said softenable layer spaced apart from said substrate in the migrated portions of said softenable layer, electrically charging the surface of the imaging member while said member is substantially uniformly exposed to activating electromagnetic radiation, and contacting said imaging member with a liquid solvent for said softenable material whereby the softenable layer and the unmigrated portions of the migration marking material are removed from said imaging member.
 3. The method of claim 1 wherein the electrical charging step comprises electrostatically charging said member.
 4. The method of claim 1 wherein said substrate is an electrically conductive substrate.
 5. The method of claim 1 wherein said substrate is substantially electrically insulating.
 6. The method of claim 1 wherein said softenable layer is of thickness in the range between about 1/2 micron and about 16 microns.
 7. The method of claim 1 wherein said photosensitive marking material comprises particles of a size not greater than about 2 microns.
 8. The method of claim 7 wherein said photosensitive marking particles are of a size in the range between about 0.02 microns and about 0.5 microns.
 9. The method of claim 1 wherein said photosensitive marking material comprises x-form metal-free phthalocyanine.
 10. The method of claim 1 wherein said migration imaging member additionally comprises a second layer comprising softenable material, said second layer disposed between the substrate and the softenable layer having the marking particles dispersed therein.
 11. An imaging method comprising: providing a migration imaging member comprising a softenable layer having electrically photosensitive marking material dispersed throughout said softenable layer, providing an electrical latent image upon said imaging member, softening the softenable layer whereby migration marking material migrates in depth in imagewise configuration in said softenable layer away from one surface of said softenable layer, then electrically charging said surface of the imaging member while said member is substantially uniformly exposed to activating electromagnet radiation, placing the opposite surface of the softenable layer in contact with a substrate, and contacting said imaging member with a liquid solvent for said softenable material whereby the migrated marking material completes its migration to the substrate in image configuration, and the softenable layer and the unmigrated portions of the migration marking material are removed from said imaging member.
 12. An imaging method according to claim 11 comprising: providing a migration imaging member comprising a softenable layer having electrically photosensitive marking material dispersed throughout said softenable layer and said softenable layer in contact with a substrate, providing an electrical latent image upon said imaging member, softening the softenable layer whereby migration marking material migrates in depth in said softenable layer toward said substrate in imagewise configuration, electrically charging the surface of the imaging member while said member is substantially uniformly exposed to activating electromagnetic radiation, and contacting said imaging member with a liquid solvent for said softenable material whereby the softenable layer and the unmigrated portions of the migration marking material are removed from said imaging member.
 13. The method of claim 11 wherein said electrical latent image is an electrostatic latent image.
 14. The method of claim 11 wherein the electrical recharging step comprises electrostatically charging said member.
 15. The method of claim 11 wherein said softenable layer is softened by exposing the imaging member to solvent vapors capable of softening said softenable layer.
 16. The method of claim 11 wherein said softenable layer is softened by the application of heat sufficient to soften said softenable layer.
 17. The method of claim 11 wherein after said softenable layer is softened, said softenable layer is substantially returned to its initial viscosity.
 18. The method of claim 11 wherein said substrate is an electrically conductive substrate.
 19. The method of claim 11 wherein said substrate is substantially electrically insulating.
 20. The method of claim 11 wherein said softenable layer is of thickness in the range between about 1/2 micron and about 16 microns.
 21. The method of claim 11 wherein said photosensitive marking material comprises particles of a size not greater than about 2 microns.
 22. The method of claim 11 wherein said photosensitive marking particles are of a size in the range between about 0.02 microns and about 0.5 microns.
 23. The method of claim 11 wherein said photosensitive marking material comprises x-form metal-free phthalocyanine.
 24. The method of claim 11 wherein said imaging member additionally comprises a second layer comprising softenable material, said second layer disposed between the substrate and the softenable layer having the marking particles dispersed therein.
 25. The imaging method of claim 1 wherein the softenable layer is substantially electrically insulating. 